Radio and optical variability in blazars

Abstract

We have investigated the statistical properties of the optical and radio monitoring observations and the correlation between the variability in these wavebands for BL Lac objects and OVV quasars. Variations between any two radio bands are well correlated with time lags measured in weeks to months. Optical variations precede radio variability with a time delay of 1–2 years with a broad correlation width of about 1 year. This demonstrates that radio components, seen to exhibit superluminal motion, are initiated by the optical activity that occurs close to the central source.

We find a significant difference in the nature of the radio and optical variability, with the former being similar to shot noise while the optical variations are halfway between shot and flicker noise. This suggests that the radio emitting plasma is not simply compact optical emitting plasma that has become transparent. Rather, significant reprocessing of the emitting plasma has occurred, such as might result through shocks or radiative losses.